July 17, 2012

Host: Ted Simons

Arizona Weather Update

An update on the drought that’s gripping the nation and a look at Arizona’s monsoon season with Randy Cerveny, a professor of geographical sciences who directs the meteorology program at Arizona State University.

Ted Simons: Arizona got a good soaking over the weekends but the state is still in a drought that's been around for the last 13 years and Arizona's not alone. More than half of the country is experiencing what is being called the worst drought since 1956, and the dry conditions keep on spreading. Joining us is Randy Cerveny, he is a professor of geographical sciences and director of ASU’s meteorology program. Good to see you again, thanks for joining us.
Randy Cerveny: Thank you.
Ted Simons: Before we get started here, what is the definition of a drought?
Randy Cerveny: [Laughs] That's actually one that’s fairly controversial. Depending on who you talk to there are different definitions. A farmer will say not having enough water to meet their crop needs. A hydrologist will say how much water do we have behind the reservoirs and use the drought to find off of that. It's dependent on upon who is talking as to what the definition is.

Ted Simons: Someone says 55% of the United States is suffering through drought conditions. What's to say they're right? What's going on out there? Why is this happening?

Randy Cerveny: Well, we can actually the way that we work with that in terms of a national determination is that state climatologists from around the country make some determinations about our particular areas and the state climatologist for Arizona is Nancy Sullenger has kind of defined that. But what has actually happened that is kind of interesting is that we're in a kind of a periodic drought cycle that a lot of people don't realize this but when you talk about the dust bowl days of the 1930s or the big drought that we had in the 1950's that there's a certain period that we see with droughts. People here at the University of Arizona tree ring laboratory have done quite extensive research across the country looking at tree ring records and they find a fairly pronounced 20-year cycle to droughts. We had it in the 30s, in the 50s, again in the '70s, again in the '90s. It's not unusual to expect we would have it this decade.

Ted Simons: Well that’s very interesting. But why would it come in these 20-year cycles? There's got to be a reason for that, isn't there?

Randy Cerveny: That's what climatologists try to figure out. Is there anything in nature that follows that same kind of cycle. And oddly enough the one thing that we can find that has a very pronounced roughly 20-year cycle is the sun spots on the sun, the type and the number of sunspots follows a 22-year cycle that corresponds very closely to the drought over the United States.

Ted Simons: Well, so corresponds but do we know why? Why would a sunspot affect weather to that degree here?
Randy Cerveny: Well, unfortunately we don't know. We can make some speculation, and the current idea is that it has to do with the amount of cosmic rays that come from the sun that changes on high sun spot years compared to low sun spot years. So the driving force on clouds and rainfall for the world seems to be how much cosmic rays we have. Therefore, if you have a variation in sunspots you vary the cosmic rays, you might vary the precipitation in some regions of the earth.

Ted Simons: So if someone is saying that Lannion or El Nino or lack of either one is playing a factor into what's happening now, would that be a secondary issue as opposed to sunspots or is Lannion a factor?

Randy Cerveny: It's a secondary factor, kind of like mother nature rolls the dice and now all the die are snake eyes. We're getting the jackpot of situations where you have just the right conditions in terms of maybe sunspots but you also then have situations in the sea surface temperatures in the Pacific, this El Nino, Lannion situation that is going on. Plus you have changes in the jetstream that can modify where the storms are actually traveling.

Ted Simons: So back to the definition of a drought, we're looking at maybe 20-year cycles, but for much of the '70s, we had some monster rainstorms that closed bridges and everyone was standing idly in their cars waiting. But with all this going on, can a drought just come up out of nowhere? How long does it have to be dry before you call it a drought.

Randy Cerveny: Uh, again that's dependent upon who you talk to. For Arizona we can come in and out of droughts fairly quickly. The amount of water that's needed to replenish the crop situation here isn't that much. We don't get that much, so it doesn't take a lot to change it. But you get into a place like Texas or Oklahoma or Kansas and it takes substantially more water to get them out of a drought situation. So that's what the big problem is. You all remember that a few years ago we had this tremendously dry situation in Texas. Frankly it hasn't gotten any better because they haven't had tropical storms coming through. So you had this going on for years and years and the soil starts to transform itself, becomes less producible.

Ted Simons: So after last week, last question here, after last week here in the valley with all that rain and all that clouds and beautiful temperatures, absolutely fantastic, do sunspots, does the drought elsewhere, is any of that a factor in the monsoon?

Randy Cerveny: No. It really isn't. The monsoon is driven very much by local circumstances. By how much heat we get and where the winds are coming from. Last week we had a very nice situation where the winds were all coming up from the Gulf of California and it just dumped on us. We had four days of rainfall. That's the first time in four years we have had four consecutive days of rainfall in Arizona.

Ted Simons: SO here's my last question then. If a drought can be a flash drought, come up quickly, can you end the drought rather quickly or is that more gradual process?

Randy Cerveny: For us, it can end fairly quickly. We can get several storms and for farmers at least a drought might be over. For people at SRP, talking about how much water is behind the reservoirs, it might take longer. For a place like Texas it takes a lot longer. They need a lot more rainfall because they need each year to have a lot more rainfall for their crops. We don't. So we can get out of a drought much faster than they can.

Ted Simons: Alright, good stuff Randy. Good to see you. Thanks for joining us.